With advances in small-incision cataract surgery, increased emphasis has been placed on developing soft, foldable materials suitable for use in artificial lenses. In general, these materials fall into one of three categories: hydrogels, silicones, and acrylics.
In general, hydrogel materials have a relatively low refractive index, making them less desirable than other materials because of the thicker lens optic necessary to achieve a given refractive power. Conventional silicone materials generally have a higher refractive index than hydrogels, but tend to unfold explosively after being placed in the eye in a folded position. Explosive unfolding can potentially damage the corneal endothelium and/or rupture the natural lens capsule. Acrylic materials are desirable because they typically have a high refractive index and unfold more slowly or controllably than conventional silicone materials.
Acrylic materials suitable for intraocular lenses are generally soft and hydrophobic and have an equilibrium water content of less than 5% by weight. See, for example, those described in U.S. Pat. Nos. 4,834,750, 5,290,892, 5,331,073, 5,693,095, 5,922,821, 6,241,766, 6,245,106, 6,313,187, 6,353,069, 6,528,602, 6,653,422, 6,703,466, 6,780,899, 6,806,337, 6,872,793, 7,585,900, 7,652,076, 7,714,039, 7,790,824, 7,790,825, 7,799,845, 7,847,046, 8,058,323, 8,362,177, 8,466,209, 8,449,610, 8,557,892 (herein incorporated by references in their entireties). However, soft hydrophobic acrylic materials can be tacky. It is generally desirable to reduce the amount of surface tack in materials intended for use as a foldable intraocular lens. Tacky materials can be difficult to manufacture, handle, and unfold. Attempts have been made to reduce tackiness so that the lenses are easier to process or handle, easier to fold or deform, and have shorter unfolding times. For example, U.S. Pat. No. 5,603,774 discloses a plasma treatment process for reducing the tackiness of a soft acrylic material. U.S. Pat. Nos. 6,241,766; 6,245,106; 7,585,900; 7,714,039 and 8,362,177 disclose use of hydrophilic components or additives for reducing the tackiness of a soft acrylic material.
In addition, a soft hydrophobic acrylic material is susceptible to have glistenings (or microvacuoles) which are formed in vivo and can affect adversely the optical performance of intraocular lenses. Glistenings are tiny inclusions of water present within the matrix of an IOL material and are visible due to differences in refractive indices between the IOL material and water within the IOL material. It is reported that a polyethylene glycol (PEG)-containing polymerizable component (monomer and/or crosslinker) (U.S. Pat. Nos. 5,693,095, 6,353,069, and 8,449,610) can be used to improve glistening resistance of hydrophobic acrylic formulations. But, in order to minimize its adverse effects on the refractive index of acrylic materials, low amounts of PEG dimethacrylate or PEG mono-(meth)acrylate concentrations are often required. Addition of PEG dimethacrylates or PEG mono-(meth)acrylates also tends to decrease the modulus and tensile strength of the resulting copolymer.
U.S. Pat. No. 6,140,438 discloses the use of a hydrophilic monomer for improving glistening resistance of soft hydrophobic acrylic materials and the use of an alkyl (meth)acrylate for improving the flexibility and the shape restoration property of soft hydrophobic acrylic materials.
U.S. Pat. Nos. 6,329,485 and 6,657,032 disclose soft, foldable hydrogel lens materials which have a water content of approximately 5 to 30 percent by weight and are made from a composition comprising two principal monomers, one aromatic high refractive index monomer and one hydrophilic (meth)acrylate monomer (e.g., hydroxyethyl methacrylate) in an amount greater than that of the aromatic high refractive index monomer.
U.S. Pat. No. 6,852,793 discloses polymeric compositions which have a water content from 4.5 to 15 percent by weight, a relatively high refractive index of approximately 1.45 or greater, and a relatively high elongation of approximately 80 percent or greater and which are produced through the polymerization of one or more copolymers with one or more hydrophilic monomers (preferably N,N-dimethylacrylamide) and optionally one or more aromatic-based monomers, hydrophobic monomers or a combination thereof.